Hi Geert,
This is a little bug in the GradientsHdrComposition process (one of the process' parameters is not being locked correctly so the PI Core application cannot access it).
While Georg fixes this, the workaround is uninstalling the GradientDomain module:
- From the main menu, go to Process > Modules > Manage Modules.
- On the Manage Modules dialog, look for the GradientDomain module in the modules list. Double click it so the green checkmark turns into a red crossmark.
- Click the Done button.
- Exit PixInsight and run it again. Now you don't have the gradient domain tools available but projects should work normally.
Unfortunately I have to travel until next Tuesday so I cannot release a new update now. Hopefully Georg will fix this issue soon in a new version of the module.